Login to your WordPress Admin area then under Appearance find Editor option. From Theme Files menu find sidebar_left.php or files related to slidebar and search for <h3>Register to Access Now</h3> and replace it with Image you want to put.

I think the Wishlist Member code is encrypted. Searching it for the target text didn't work. I wanted to change the punctuation in the widget and make a minor wording change to match the rest of my site, but have been stymied. Perhaps in a future release users will have this option.

I can't recommend WishList. I have it. It installed easily - but the whole point of WishList is being able to charge members and have them register. For 2 months I struggled with WishList asking for support - and their response was only to send me all the information I had already tried based on the videos and .pdf books they had. Nothing was working and they weren't stepping in to assist me with real help. So I hired a tech guy - and he saw the problem. Finally WishList provided the code, but after 2 months of struggling and literally begging them to help me, and spending $360 for a tech guy to figure it out, I CANNOT RECOMMEND WISHLIST! Their support was abysmal and basically none existent and the fact that I could not sell my product or get my product up for over 2 months costs me thousands of dollars of revenue. (My package goes for $1,497). Next time I buy something that has better support.